1997 v70 T5 Stutter at WOT on T5

Post by **Fiodor** » 18 Feb 2021, 11:00

Hello dear Volvo people !

My list of Volvo woes keeps getting longer it seems.

The issue:

My V70 T5 developed a stutter at WOT some time ago.

Resetting the ECU removes the stutter until the car is turned off and restarted.
Checking the ECU didn't yield any codes.

About the car:
It's a V70 T5M from 1997 with the Italian B5204T3 (2.0L making 225hp). It's got 250 000 km on it.

Ignition:
Spark plugs are Volvo and 2 years old, so are the spark wires. Distributor and rotor were replaced along with the plugs.
Battery is new, alternator gives around 13.5V when lights/defrost/AC are on.

Injection:
Injectors are original, I replaced the O-rings and the filters to no avail 1 week ago.

Vacuum:
I've checked for vacuum leaks using a good ole' cigar, found 2 which I fixed (got a lung cancer in the process but what wouldn't we do for our cars?)

Intake:
I've got a RIP kit from do88 installed on the car, every air tube/duct/hose has been triple checked by me/my father/my friends/the neighbours/some random stranger who wondered why my hood was open in the street.

Car has been running on E85 without issues for the past 2 years, I haven't reprogrammed the ECU (boooo I know, I just need the money!) so I've been using a piggyback device.

If you have an idea please share it with me!
You can also just send positive thoughts and prayers to prevent me from going into Volvo depression

Post by **Goupil** » 18 Feb 2021, 11:40

Have you checked the fuel pressure under load

I had an issue of the engine falling on its face at WOT, it was a bad clamp on the fuel hose between the pump and the carrier inside the tank.

Post by **Fiodor** » 18 Feb 2021, 11:58

Hmm, how would I go about doing that ?

Post by **ZionXIX** » 18 Feb 2021, 17:21

Get a fuel pressure gauge and connect to the fuel rail end. Rev the throttle manually in the engine bay while watching the gauge to see if it drops.

Post by **matthew1** » 18 Feb 2021, 20:32

Fiodor wrote: ↑18 Feb 2021, 11:00 ...I've been using a piggyback device.

Have you removed that to test?

How is your battery? What's the age, brand/quality?

Post by **Fiodor** » 19 Feb 2021, 02:40

Battery is brand new, Fulmen 640A and 64 Ah.
I haven't removed the piggyback thingy, once my tank's empty I'll switch to regular gas and remove the piggyback apparatus.

Post by **Fiodor** » 27 Feb 2021, 09:39

Piggyback removed, front lambda sensor replaced, new pierburg tcv installed, new Bosch injectors.
Everything is the same as before (lambda and Injectors fixed some stumbling at idle) ie. drove perfectly fine for 15km after resetting the ECU and then the hesitation at WOT came back.
Still haven't checked the fuel pressure but I don't see how that would explain the fact that the engine runs fine when the ECU just got reset.

It's boosting consistently at 0.9 bar without any spikes.
One thing that's been puzzling me is that my fuel trims are stuck at 0% (using torque pro and xanthefin's app 850-OBDII).

Post by **Fiodor** » 27 Feb 2021, 09:40

Oh and I'm also back to regular gasoline.

Post by **Goupil** » 28 Feb 2021, 03:53

Fiodor wrote: ↑27 Feb 2021, 09:39 One thing that's been puzzling me is that my fuel trims are stuck at 0% (using torque pro and xanthefin's app 850-OBDII).

Sounds like the ECU is sticking to open loop

Maybe a bad O2 sensor ?

Post by **Fiodor** » 28 Feb 2021, 05:03

I replaced the front O2 sensor with a bosch universal one yesterday.
Fixed some stumbling at idle but didn't improve the stutter condition.
And monitoring shows that the car stays in closed loop when I'm not pressing down on the gas pedal too hard.